A hydroformylation reaction producing linear (normal) and branched (iso) aldehyde which has one more carbon atoms than olefin by reacting carbon monoxide (CO) and hydrogen (H2) that are commonly called as a synthesis gas in the presence of a homogeneous organicmetalic catalyst and a ligand was originally discovered by Otto Roelen in Germany in 1938.
In general, the hydroformylation reaction that is known as oxo reaction, is a very important industrial reaction in view of a homogeneous system catalyst reaction. Currently, about 9,600,000 tons of adhehydes (including alcohol derivatives) are produced by the oxo process all over the world (SRI report, September 2006, 682. 7000 page 7).
Various types of aldehydes produced by the oxo reaction are oxidated to carboxylic acids or hydrogenated to alcohols. In addition, aldehydes can also be converted to long alkyl chain-containing acids or alcohols through aldol condensation and then oxidation or reduction. In particular, hydrogenation alcohol of aldehyde, which is obtained by the oxo reaction, as is called oxo alcohol. Oxo alcohol is industrially extensively used as a solvent, additive, various types of raw materials of plasticizers, or synthetic lubricants.
It is known that a metal carbonyl compound catalyst has a catalytic activity of the hydroformylation reaction, and almost focused on cobalt (Co) rhodium (Rh). The N/I (ratio of linear (normal) to branched (iso) isomers) selectivity, activity, and stability of aldehydes vary according to the type of ligand used and operating conditions.
To date, a rhodium-based low-pressure oxo process (LPO process) has been adopted in at least 70% of oxo plants worldwide because of the high efficiency, high yield of normal products, and mild reaction condition even though there are disadvantages of the expensive catalyst and catalytic deactivation due to the poisoning.
A central metal of oxo metal may be used a transition metal, such as iridium (Ir), ruthenium (Ru), osmium (Os), platinum (Pt), palladium (Pd), iron (Fe), or nickel (Ir). In respects to the transition metals, it is known that the order of the catalytic activity is Rh>>Co>Ir, Ru>Os>Pt>Pd>Fe>Ni and the like.
Pt and Rh as Group 8 transition metal have been mainly used in an oxo process, for example, HCo(CO)4, HCo(CO)3PBu3 and HRh(CO)(PR3)3. Pt and Ru are mainly subjects of academic interest. Therefore, Co applied for academic research, and currently most of oxo processes having industrial objects basically uses rhodium and cobalt, and a representative example may include HCo(CO)4, HCo(CO)3PBu, and HRh(CO)(PR3)3.
Examples of the ligand that is used during the oxo process include phosphine (PR3, R is C6H5, or n-C4H9), phosphine oxide (O═P(C6H5)3) and phosphite. In case of using rhodium as the central metal, it is known that the ligand having the catalytic activity and the stability that are better than those of triphenylphosphine (TPP) is almost not present. Thus, in most oxo process, rhodium (Rh) metal is used as a catalyst and TPP is used as a ligand. In addition, to increase the stability of a catalytic system, TPP ligand is used in an amount of at least 100 equivalent of the catalyst.
Since the value of linear aldehyde derivative is generally high among aldehydes that are products of the oxo reaction, many studies have been made to increase the ratio of the linear aldehyde in respects to the catalyst. However, recently, products obtained by using iso-aldehyde as the raw materials instead of the linear aldehyde, for example, an isobutyric acid, neopentyl glycol (NPG), 2,2,4-trimethyl-1,3-pentanediol, isovaleric acid and the like have been developed, thus the use of iso-aldehyde has been increased. Accordingly, there is a demand to develop a technology of producing iso-aldehyde required in a market by desirably controlling the N/I selectivity while the excellent catalytic activity and stability, together with reduced amount of ligand.